The aim of this study is to evaluate efficacy, safety, and pharmacokinetics of GLWL-01 in the treatment of patients with Prader-Willi Syndrome (PWS).

Participants will be assigned to one of two treatment sequences (GLWL-01/Placebo or Placebo/GLWL-01), with each sequence consisting of two treatment periods separated by a washout period

Inclusion Criteria:

• Confirmed diagnosis of PWS based on genetic confirmation using DNA method
• Body mass index (BMI) of 27 to 60 kg/m2
• No evidence of weight excursion beyond 10% of baseline weight
• Patients must provide assent and have a reliable caregiver (must have been caring for the patient for at least 6 months) who provides a separate written informed consent to participate. The caregiver is expected to be the primary caregiver throughout the study and must be in frequent contact with the patient (defined as at least 4 awake hours per day). The caregiver must be able to communicate with site personnel and in the investigator's opinion must have adequate literacy to complete questionnaires. If a caregiver cannot continue, 1 caregiver replacement is allowed
• Are on a stable diet and exercise regimen for >2 months prior

Exclusion Criteria:

• Current enrollment in or discontinuation within the last 30 days from a clinical trial involving any investigational drug or device

• Are currently living in a group home for more than 50% of the time

• A history or presence of other medical illness that indicates a medical problem that would preclude study participation

• Have an estimated glomerular filtration rate <60 mL/minute/1.73 m2. Have macroalbuminuria (defined as spot urine albumin to creatinine ratio of >300 μg/mg) or hematuria

• Are hypertensive (defined as sitting systolic blood pressure (BP) greater than or equal to (≥)140 millimeters of mercury (mmHg) and diastolic BP ≥90 mmHg)

• Patients on weight loss medications within 30 days of dosing, or with a history of bariatric surgery

• Unable to refrain from or anticipates the use of:

  1. Any drugs known to be significant inhibitors of Cytochrome P450, family 3, subfamily A (CYP)3A enzymes and/or P-glycoprotein (P-gp) including regular consumption of grapefruit or grapefruit juice for 14 days prior to the first dose. Acetaminophen (up to 2 grams per 24-hour period) may be permitted
  2. Any drugs known to be significant inducers of Cytochrome P450, family 3, subfamily A (CYP3A) enzymes and/or P-gp, including St. John's Wort
  3. Any medications that prolong the QT/QTc interval, unless the participant has been stable on the medication for at least 3 months and has a corrected QT interval (QTc) <450 msec

• Currently taking simvastatin >10 mg per day, atorvastatin >20 mg per day, or lovastatin >20 mg per day, or have a history of statin-induced myopathy/rhabdomyolysis

• Unsuitable for inclusion in the study in the opinion of the investigator

Up to 18 weeks

Treatment-emergent adverse event: An untoward medical occurrence that emerges during a defined treatment period, having been absent pretreatment, or worsens relative to the pretreatment state, and does not necessarily have to have a causal relationship with this treatment.